Clamp mechanism for rotary car dumper

ABSTRACT

A railroad car is secured for dumping in a rotary car dumping cradle by gravity lowered clamp beams which engage the top of the car and are locked in place by a gravity actuated, infinitely variable locking mechanism that grasps tension members connected to the side of the car dumper.

O United States Patent 1 1 3,796,329

Ouska Mar. 12, 1974 CLAMP MECHANISM FOR ROTARY CAR BUMPER Primary ExaminerRobert G. Sheridan [75] Inventor: Ralph c. Ouska, Hinsdale, In. 122x 31 1 52' Q.. ""T 92? Y? h?j," C: [73] Assignee: FMC Corporation, San Jose, Calif.

[22] Filed: May 12, 1972 [21] Appl. No.: 252,731 v [57] ABSTRACT Related US. Application Data [62] Division of No 135,960, April 21, 1971 PM A railroad car is secured for dumping m a rotary car No. 3,719,291 dumping cradle by gravity lowered clamp beams which engage the top of the car and are locked in 52 US. Cl. 214/55 place y a g y actuated, infinitely variable locking 51 Int. Cl. B65g 67/54 mechanism that grasps tension members connected to 58 Field of Search 214/55, 56 the side of the car p [56] References Cited 4 Claims, 17 Drawing Figures UNITED STATES PATENTS 1,465,006 8/l923 Simpson e! a]. 2l4/55 X 1 l8 5 i ,210 20 N 226 l I I v land; 220ml ZIO'Q PATENIEBmmm 3796329 SHEEI 8 BF 8 F'I I3 CLAMP MECHANISM FOR ROTARY CAR DUMPER This application is a division of U.S. application Ser. No. 135,960 filed Apr. 21, 1971, now Pat. 3,719,292.

BACKGROUND OF THE INVENTION The present invention relates to clamping devices for a rotary railroad car dumper. More particularly the present invention relates to mechanisms for automatically positioning and locking a railroad car clamping device in a rotary car dumper.

Modern systems for bulk handling of various material such as coal, coke, wood chips or the like generally make use of a car dumper machine for rapidly unloading railroad cars individually, in groups or by the train. Railroad siding tracks pass through the machine to enable a single car or group of cars to be stopped and held inside a cradle that can be rotated to turn the railroad car over and empty its contents into a hopper below.

Various clamp mechanisms have been employed to hold the car from falling away from the track and supporting table while it is being turned over. Many combinations of cable, sheaves, racks, drums, chains, band brakes, hooks, ratchets and pawls have been employed to lift and hold clamping beams and hooks in contact with the railroad car body. Gravity, electric motors, hydraulic cylinders and the motion of the car dumper have been used to provide power to operate these mechanisms.

One device presently in use, which is described in U.S. Pat. No. 1,606,453 to Simpson, includes a car dumper having individually actuated hook members that slide downwardly into engagement with the sides of a railroad car under the influence of a sheave and rope arrangement. Once the car is engaged, the hooks are individually locked by locking mechanisms comprised of alternate friction plates and clamp bars that are forced into frictional locking engagement during dumper rotation by the coaction of a series of wedges and rollers actuated by a counterweight. Another mechanism for clamping a railroad car in a rotary car dumper, as described in U.S. Pat. 1,609,420 to Norris,

utilizes gravity lowered clamping hooks which are locked into engagement with a railroad car by a locking mechanism having jaws forced together by togglelinkage to grasp a vertical bar. The toggle-linkage of this device is actuated by a cable and sheave arrangement.

In all cases, positive operation of the locking clamps is an object of high priority because of the possible disastrous results if the clamps are not firmly locked as the loaded cars are inverted. This problem is particularly acute in some environments. For example, the contents of coal or ore cars operating in extremely cold climates sometimes freeze solid to the body of the car and will not dump when inverted. This places the gross weight of the loaded car, a weight of perhaps 200 to 300 tons directly onto the locking clamps. Thus, while safe locking clamps are an absolute requirement for all rotary car dumpers, the attainment of a safe locking clamp system without directly or indirectly applied power actuation has heretofore been limited to car dumpers which operate under conditions more favorable than extremely cold climate use where counter-weighted locking clamps might be prone to malfunction.

The car clamp systems now in use have either all or many of the following disadvantages. They are complex mechanisms, subject to jamming, which are difficult and costly to build and install and which require frequent maintenance and adjustment. Some require auxiliary power, while some require duplicate or back up components to assure safety under severe load conditions.

Accordingly, a general object of the present invention is to provide locking clamps which are automatically operable and safe in all, including sub-zero, temperatures.

A further object of the invention is to provide a clamping arrangement with less complex structural and mechanical components, with less wear and less need for adjustments and with no requirements for auxiliary power.

Another object of the invention is to provide a positive means of lowering a clamping mechanism into engagement with a railroad car.

A further object of the invention is to provide a means within a railroad car clamping mechanism for relief of forces created by the compression in railroad car truck springs.

SUMMARY OF THE INVENTION In the present disclosure, a car clamp is provided which is positioned and locked only by gravitational forces. These forces are exerted during rotation of the cradle without reliance on auxiliary power or force transmitting cable and with minimum linkage. In the preferred form of the invention, beam clamps initially held in elevated position by a stationary post, are loweretl along guides by the action of gravity during the dumping cycle to hold a railroad car in place in a rotary car dumper cradle. As the dumper is rotated, the beam clamps drop into contact with the top of the car, and once in place atop the car, the clamps are locked in that position. The locking mechanism utilized to lock the clamps in place is activated by the action of gravity, as are the clamps, so that no power source, other than that used to rotate the cradle, is necessary. An actuating weight mounted at the end of a lever, which changes its moment direction as the dumper is rotated, supplies the force necessary to actuate the lock. A clamp bar assembly of the lock mechanism is defined by a series of spaced plates interspersed between a series of parallel spaced metal strips that are connected to the side of the cradle and are slidable relative to the spaced plates when the lock mechanism is unlocked. As the cradle is rotated beyond 35 of rotation toward the dumping position the weight moment shifts, causing a series of toggle links, which are interconnected with the actuating weight lever, to extend. The extension of the toggle links forces the plates of the lock mechanism into very tight locking contact with the strips of the clamp bar assembly to hold the beam clamps in position on top of the car during the dumping cycle. Thus, the clamp is always lowered and locked by gravity forces, and there are no cables to break or jam.

The present invention is directed to the relief of truck spring compression forces.

DESCRIPTION OF THE DRAWINGS mechanism of the present invention with parts removed.

FIG. 5 is a fragmentary horizontal section taken along line 5--5 of FIG. 2 showing the upper guide rollers of the clamp hook assembly.

FIG. 6 is a fragmentary horizontal section taken along line 6-6 of FIG. 2 as viewed from below showing the guide rollers on one side of the clamp assembly.

FIG. 7 is a fragmentary side elevation of the locking mechanism of the present invention with portions being broken away.

FIG. 8 is a horizontal section of the locking mechanism taken along line 8-8 of FIG. 7.

FIG. 9 is a vertical section of the locking mechanism taken along line 9-9 of FIG. 7.

FIGS. 10, 11, 12 and 113 are diagrammatic end elevations of the apparatus shown in FIG. 1, in four operational positions.

FIG. 14 is an end elevation of the clamp mechanism of another embodiment with parts broken away.

FIG. 15 is a plan view of the clamp mechanism of FIG. 14.

FIG. 16 is an enlarged vertical section taken along line 16-16 of FIG. 14.

FIG. 17 is a diagrammatic perspective with parts removed of the clamp mechanism incorporating the truck spring relief apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 3, there is shown the general organization of the preferred form of the invention in which a railroad car R is supported within a rotatable cradle structure of a rotary car dumper 32. The open-top car R is held for rotation within the cradle structure 30 by two clamp mechanisms 34. The cradle structure 30 is rotated by a drive system 36 into position to dump the contents of the railroad car down a chute 31.

More specifically, the cradle 30 of the rotary car dumper 32 is an essentially U-shaped structure. The U-shaped cradle 30 is constructed of longitudinal horizontal beams 38, 40 and 42 that are rigidly secured be tween a pair of circular ends 44 and 46, vertical beams 48 and 48a and diagonal members 50 and 50a secured between the horizontal members to give structural rigidity to the cradle structure, and cross beams 52 that extend transversely between the lower horizontal members 42. A platform 54 that extends the length of the cradle structure and through openings 58 in the circular ends is supported on parallel support beams the platform 54 and support the car R for movement into and out of the cradle through the openings 58. The rails 64 are in linear alignment with rails 66 on the surface inlet and discharge sides of the pit.

Cradle 36 is supported for rotation on four rollers 68 which are rotatively supported on support members 70 anchored in the base of the pit. Tracks 71 extend partially about the periphery of each of the circular ends 44 and 46 and mate with the rollers 68 that support the cradle in rotation.

Power for rotating the cradle 30 is supplied by a reversible electric motor-gear reducer unit M (FIG. 1) which has power shafts '72 each of which terminates near one of the cradle ends 44 and 46. A pinion gear (not shown) at the end of each shaft '72 drives a large ring gear (not shown) which is part of a cable winch 74. A cable 76 of each winch is spirally wound on a drum 78 of the winch 74 and has ends secured by anchors 79 to the respective cradle ends 44 and 46 for rotation of the cradle 36 to the dumping position, and for the return of the cradle from the dumping position, as the. motor unit M is energized.

The clamping mechanisms 34 are supported within the cradle 30 by two vertical support members or trusses 82 which are secured to the horizontal beams 38, 40 and 42 neareach of the circular ends 44 and 46. Each of the support members 82 is constructed of beams 82a secured together in a spaced parallel orientation to present a slot 84 (FIG. 8) therebetween.

Each of the clamping mechanisms or car securing members 34 is identical in structure to the other and functions independently of the other. Each clamping mechanism includes a carriage 88 having an upright member 90 (FIG. 2) mounted for endwise movement on a pair of rails 86, an upper transverse member 92 rigidly secured to the upright member 90 and extending inwardly of the cradle, a lower transverse member or lift beam 94 rigidly attached to the upright member 90 and extending outwardly from the cradle'through the slot 84 in the vertical support member 82, and a clamp beam 96 suspended from the upper transverse member, a clamping element 98 (FIG. 7) secured at either end to the truss 82 and extending vertically in the slot 84 of vertical support member 82, and a vertically extending post or lift member 100 secured to the surface adjacent the cradle structure.

The upright member 90 (FIGS. 2, 6 and 7) is an elongated rectangular structure that engages the rails 86. A combination of rollers and bearing bars attached to the upright member 90 contact the rails 86- and guide movement of the upright member 96 relative to the rails 86. The rollers are positioned for maximum contact with the rails 86 as the cradle overturns. At the top of the upright member 90 one pair of rollers 102 are positioned (FIGS. 2 and 5) such that they contact the inner edges of rails 86. A second pair of rollers 104, attached near the top of the upright member 90, is positioned to engage the rear surfaces 86a of the rails. A pair of bearing bars 106 secured to the upright member abut the opposite or front faces 86b of the rails 86 and provide a secondary contact surface as the upright member moves relative to the rails 86.

A pair of rollers 168 (only one being shown in FIGS. 2 and 6) secured to the lower end of the upright member 90 engage the front faces 86b of the rails 86. Another pair of rollers I10 (FIGS. 2 and 6), mounted on brackets 112 at the lower end of the upright member 90, follow the outer edges of rails 86. Bearing bars or shoes 114, (FIG. 6) which are secured to the lower portion of the upright member 90, contact the back faces 86a of rails 86.

The upper transverse arm 92 is constructed of spaced parallel plates 92a (FIG. 2) which are rigidly secured at one end to the upright member 90. At the other end of the transverse arm 92, clamp beam 96 is disposed in a slot between the plates 92a on a pivot pin 116 that extends through the plates 92a. Pivot pin 116 is retained at the ends by collars 116a secured to the plates 92a and to the pin 116. The clamp beam 96 which is pivoted at its center on pin 1 16 includes a horizontal center portion 96a and arms 96b extending diagonally downwardly from the horizontal portion. Clamp pads 118 and 120 are secured to arms 96b for engagement with the sides of an open-top car R. Vertically disposed channel members 122 (FIG. l), which are secured to the cradle opposite the vertical support members 82, serve to guide the outer contact pads 120 as the clamp beam 96 moves up or down relative to the cradle 30.

The lower transverse arm 94 includes a pair of beams 94a (FIGS. 2 and 8) rigidly secured in spaced, parallel relationship. A roller or cam 124 is secured for rotation on a shaft 126 between the outer ends of the beams 94a. The roller 124 contacts an inclined upper surface of the vertical post 100 when the cradle is in the upright position.

A locking mechanism 128 that engages the clamping element 98 is secured between a pair of clamp brackets 134 (FIG. 9) that overlie the beams 94a. The clamp brackets 134 are rigidly secured to the upper surface of the beams 94a. Hold down brackets 135 are secured between the clamp brackets 134 and the upright member 90 to add structural rigidity.

Referring to FIGS. 2, 3, 4, 7, 8 and 9 the locking mechanism or gripping member 128 is illustrated in its preferred form. In general the locking mechanism consists of interconnected linkage 129 which is actuated during cradle rotation by the change of position of actuating weight 130 to force a series of spaced pressure plates 132 into frictional locking engagement with a series of elongated strips 98a of the clamping element bar assembly 98.

More specifically, locking mechanism 128 which is contained within the clamp brackets 134, includes the series of spaced pressure plates or second contact members 132 that are interspersed between elongated strips or first contact members 98a of the clamp bar assembly 98 as illustrated by FIGS. 4 and 7. The elongated strips 98a are permanently spaced at the upper and lower points of connection by spacers 136 (FIG. 3) which are placed between alternate strips 98a on connection shafts 137. The pressure plates 132, which are slidable relative to the strips 980 when the locking mechanism 128 is unlocked, are held and restrained from movement relative to the lock mechanism by the clamp brackets 134 (FIG. 9). A spacer or pressure block 138, (FIG. 4), which is a rectangular block bolted between clamp brackets 134, maintains the spacing of the clamp brackets 134 and provides a fixed abutment against which the pressure plates 132 and strips 98a are forced during clamp locking.

The toggle linkage 129 (FIGS. 4 and 7), which is actuated to force the pressure plates 132 and strips 98a into locking engagement, includes a pivot block 140 that is pivotally anchored on shaft 142 to clamp brack ets 134. Shaft 142 is retained at its ends by keys 142b that are secured to the clamp brackets 134. Four fingers 140a of the pivot block 141) extend to the left (FIGS. 4 and 8) and pivotally interdigitate with a pair of toggle links 144 and lever link 146 which are on a common shaft 148. Shaft 148 is retained at its ends by the machined inner surfaces of the clamp brackets 134. A stop member 150 of shock cushioning material limits the upward travel of the toggle linkage when the lock mechanism is in the released position of FIG. 7.

The left ends (FIGS. 4, 7 and 8) of the two links 144 extend into parallel slots 152a in pressure block 152. The pressure block 152 is a rectangular metal block having a machined exterior and having an indentation 15% formed on one face to receive a pressure plate 154 that is bolted to the pressure block 152. The ends of links 144 which extend into slots 152a are rigidly secured to a shaft 156 that extends through the pressure block 152 and is bushed for rotation therein. Pressure block 152 is retained by the machined inner surfaces of clamp brackets 134 which provide a bearing surface for sliding movement of the pressure block 152. The ends of shaft 156 are also retained by the inner surfaces of clamp brackets 134.

The lower end of link 146 (FIGS. 4 and 7) is pivotally connected to an actuating lever 158 to which the actuating weight or element 130 is attached. Lever 158, which is constructed of spaced parallel plates 1580 (FIG. 4), is pivoted on a shaft 160 that is anchored to lift beam 94 by means of keys 160a (FIG. 2). Link 146 is disposed for movement in the slot between the parallel plates 158a and is pivoted on shaft 162 which is fixed at its ends to plates 158a.

Having thus described the structure of the preferred embodiment of the invention, its operation can now be explained. When the dumper 32 is in its initial upright position (FIG. 18) with the railroad car R upright, the clamp beam 96 is held up clear of the railroad car. The roller 124 at the end of beam 94 is in contact with the inclined upper surface of the lift post when the dumper is in this initial position and the clamp locking mechanism 128 is unlocked. Once the railroad car R is positioned properly inside the dumper cradle 30 the dumper motor M is energized causing the cradle to rotate in a counterclockwise direction about a longitudinal rotational axis L towards the dumping position. As rotation proceeds the carriage 88 holding the clamp beam 96, which is above and clear of the car (FIG. 10), begins to drop by its own weight due to the force of gravity. The clamping mechanism 34 continues to drop uniformly with the roller 124 in contact with lift post 188 until the clamp beam 96 contacts the top edges of the car sides, whereupon clamp lowering stops. Rotation continues and the roller 124 loses contact with the lift post 100. At about 35 cradle rotation (FIG. 1 1) the center of gravity of the clamp lock actuating weight 136 passes directly over the pivot point of the actuating lever 158 with a consequent change in the moment direction of the weight from a clockwise to a counterclockwise direction. As the moment direction of weight 130 changes, tension is placed on the lever link 146. The lever link 146 in turn transfers the actuating weight moment to shaft 148 tending to bring the fingers 1400 of pivot block and the toggle links 144 to a more linear orientation. This causes the extended toggle links 144 to force pressure bracket 152 to the left (FIGS. 4 and 7), transmitting pressure to the pressure plates 132, the clamp bar assembly 98 and the pressure block 138. The pressure plates 132 and the strips or bars 98a of the clamp bar assembly 98 are thus forced into a very tight frictional engagement which stops the sliding motion of the pressure plates 132 relative to the clamp bar assembly 98a and locks the clamp beam 96 against the top edge of the car R.

As the dumper continues to rotate the actuating weight 130 moment keeps the lock tightly engaged. Material in the car begins to fall out (P16. 12) as the car overturns and the dumping process is usually completed by the time the dumper has rotated to the 160 position. The material falling from the car drops into chutes 31 below the cradle which conduct the material to below ground conveyors. After all material has been dumped, or when 180 rotation (FIG. 13) is reached,

the dumper motor M is reversed. The car springs which were originally compressed by the load of the material on the car are now held in compression by the clamps 96 which are locked in place. As the 35 point is approached on the return cycle, the actuating weight moment diminishes, reducing the clamp locking pressure to the point at which the pressure plates 132 will again slip in relation to the bars 98a of the clamp bar assembly 98 and gradually release the compression of the railroad car springs. Below 35 of rotation, the clamp lock 128 is fully released as the roller 1124 again contacts the upper face of the lift post 100. With roller 124 in contact with post 100, as the cradle rotates to the starting position, the carriage 88 is urged uprwardly relative to support member 82, and the clamp beam 96, which is swung from the carriage 88, is lifted out of contact with car R. As the upright position is again reached, rotation and upward lifting of the clamp mechanism 80 stops and the railroad car R is ready to be moved out of the dumper 32. If the dumper 32 is to be rotated without a car R in place, all operations are the same except that the clamp 96 travels to a stop at a minimum car height and the lift roller 124 moves off of the lift post 100 at about 35 rotation of the cradle.

Another embodiment of the present invention incorporates mechanism for relief of the compressed truck springs of a rail car into a clamping mechanism 206 similar to that previously described. The clamping mechanism 206 of this embodiment includes a carriage having an upright member 208 engaged for movement relative to the cradle, an upper transverse member 210 from which a clamp beam 212 is suspended, a lift beam having a roller at its outer end in contact with a lift post, and a mechanism 214 for relieving the force of compression of rail car truck springs on the clamping mechanism. The lift beam and lift post of this embodi-' ment are identical to the lift beam and lift post described in the first embodiment and are not shown in the illustrations of this embodiment.

The clamp beam 212 of this embodiment is suspended on shaft 216 between spaced, parallel arms 210a of the transverse member 210. Spring yoke 218 is situated at the central portion of the clamp beam 212 with a lower section of the yoke 218 depending into a trapezoid-shaped slot in the beam 212. Shaft 216 extends through yoke 218, through vertically slotted holes 2120 (FIGS. 14 and 16) in the parallel sides of clamp beam 212, and is anchored at its ends to the parallel arms 210a of transverse member 210 by keys 220. A pair of spherical-shaped elastomeric springs or resilient elements 222 are secured as by bolting between horizontal plates 224 of spring yoke 218 and plates 226 on the upper surface of the clamp beam 212.

To illustrate the problem of truck spring compression on the beam clamps, consider the dumping operation of a car R which weighs 60 tons unloaded and which carries a 60 ton load. As the car is rotated to the dumping position and the 60 ton load is dumped, the truck springs on the car will transfer a force equal to the 60 ton load to the beam clamps even though the load has been dumped. This situation occurs because the springs were compressed by the load as the clamps were lowered. The springs exert an upward force which neutralizes the downward force exerted by the upright, loaded car, but, as the car is rotated, the force of the springs, as well as the load in the car and the weight of the car itself, are shifted to the clamps. If the load dumps properly, a ton load will be exerted on the clamps (the weight of the car plus the force created by the springs). However, if the load should stick to the car an extra 60 ton load will be placed on the clamps giving a cumulative ton load on the clamps. The object, then, of this embodiment of the invention is to relieve the load on the clamps that is created by spring compression.

In operation, a loaded railroad car R is placed in the car dumper and a motor is energized to rotate the dumper to the dumping position. Clamping mechanism 206 lowers by gravity with the rotation of the dumper until clamp 212 contacts the top of car R. At this point, the clamp lowering stops because shaft 216 is already at the top of slots 212a in clamp beam 212. As rotation continues to the 35 point, the clamp mechanism locks the clamp beam in position. As the car is rotated from its initial position to the dumping position, the weight of the car, its load, and the force of the compressed springs transfer to the clamp beam. When this occurs the spherical-shaped, elastomeric springs 222 are compressed or flattened to absorb the force of the com pressed truck springs as clamp beam 212 is pushed in a direction away from the top of car R by the force from the truck springs. The clamp beam 212 moves relative to the upper transverse member 210 and shaft 216. Consequently, the compressed railroad car truck springs extend to maintain the car in contact with the clamp beam. The force exerted on the clamp beam 212 by the compressed truck springs is thus alleviated with the extension of the truck springs and the transfer of the spring compression to the elastomeric springs 222.

Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention.

What is claimed is:

1. In a rotary car dumper having a rotatable frame to support a car for rotation between an upright position and a dump position and having a carriage which can be clamped to the frame in a selected position, the combination comprising a clamp beam mounted to the carriage for limited vertical movement with respect thereto, a yoke secured to the carriage and having a pair of arms extending outwardly over the clamp beam, and at least one spring interposed between each yoke arm and the clamp beam to urge the clamp beam to one extreme position with respect to the carriage.

2. In a rotary car dumper having a rotatable cradle to support a car for rotation between an upright position and a dump position and having a carriage which can be clamped to the cradle in a selected position, the combination comprising a clamp beam mounted to the carriage for limited vertical movement with respect thereto, said clamp beam extending over the body of the car for clamping contact therewith, a yoke secured to the carriage and having a pair of arms extending outwardly over the clamp beam, and at least one compression spring interposed between each yoke arm and the clamp beam to urge the clamp beam to one extreme position with respect to the carriage.

3. In a rotary car dumper having a rotatable cradle with means to support a car in a predetermined position in the cradle for rotation between an upright position and a dump position, the combination comprising a carriage slidably mounted on the cradle, said carriage having a transverse member extending over said predetermined car position, means to clamp said carriage in a selected position, a clamp beam mounted to said transverse member for limited vertical movement with respect thereto, said clamp beam extending across the entire width of the car for clamping contact therewith, a yoke pivotably secured to the transverse member in a substantially centered position with respect to said predetermined car position, said yokehaving a pair of arms extending outwardly over the clamp beam, and two compression springs mounted, respectively, between said yoke arms and said clamp beam to urge the clamp beam to its lowermost position with respect to said transverse member, said clamp beam yielding upwardly against the force of said springs as the car rises in the cradle after a load is dumped.

4. In a rotary car dumper having a rotatable frame to support a car in a predetermined position for rotation between an upright position and a dump position, the combination comprising a carriage, means to clamp the carriage on the frame in a selected position, a clamp beam mounted on said carriage for limited vertical movement with respect thereto, said clamp beam extending across the entire width of a car in said predetermined position for clamping engagement with both sides thereof, means on said carriage to support a pair of springs, and a pair of springs mounted between said support means and said clamp beam to urge the clamp beam to its lowermost position with respect to said carriage for yielding movement of the clamp beam against the force of said springs as the car rises after the load is dumped therefrom. 

1. In a rotary car dumper having a rotatable frame to support a car for rotation between an upright position and a dump position and having a carriage which can be clamped to the frame in a selected position, the combination comprising a clamp beam mounted to the carriage for limited vertical movement with respect thereto, a yoke secured to the carriage and having a pair of arms extending outwardly over the clamp beam, and at least one spring interposed between each yoke arm and the clamp beam to urge the clamp beam to one extreme position with respect to the carriage.
 2. In a rotary car dumper having a rotatable cradle to support a car for rotation between an upright positiOn and a dump position and having a carriage which can be clamped to the cradle in a selected position, the combination comprising a clamp beam mounted to the carriage for limited vertical movement with respect thereto, said clamp beam extending over the body of the car for clamping contact therewith, a yoke secured to the carriage and having a pair of arms extending outwardly over the clamp beam, and at least one compression spring interposed between each yoke arm and the clamp beam to urge the clamp beam to one extreme position with respect to the carriage.
 3. In a rotary car dumper having a rotatable cradle with means to support a car in a predetermined position in the cradle for rotation between an upright position and a dump position, the combination comprising a carriage slidably mounted on the cradle, said carriage having a transverse member extending over said predetermined car position, means to clamp said carriage in a selected position, a clamp beam mounted to said transverse member for limited vertical movement with respect thereto, said clamp beam extending across the entire width of the car for clamping contact therewith, a yoke pivotably secured to the transverse member in a substantially centered position with respect to said predetermined car position, said yoke having a pair of arms extending outwardly over the clamp beam, and two compression springs mounted, respectively, between said yoke arms and said clamp beam to urge the clamp beam to its lowermost position with respect to said transverse member, said clamp beam yielding upwardly against the force of said springs as the car rises in the cradle after a load is dumped.
 4. In a rotary car dumper having a rotatable frame to support a car in a predetermined position for rotation between an upright position and a dump position, the combination comprising a carriage, means to clamp the carriage on the frame in a selected position, a clamp beam mounted on said carriage for limited vertical movement with respect thereto, said clamp beam extending across the entire width of a car in said predetermined position for clamping engagement with both sides thereof, means on said carriage to support a pair of springs, and a pair of springs mounted between said support means and said clamp beam to urge the clamp beam to its lowermost position with respect to said carriage for yielding movement of the clamp beam against the force of said springs as the car rises after the load is dumped therefrom. 